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bpf: support fsession for bpf_session_cookie

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Implement session cookie for fsession. The session cookies will be stored
in the stack, and the layout of the stack will look like this:
  return value	-> 8 bytes
  argN		-> 8 bytes
  ...
  arg1		-> 8 bytes
  nr_args	-> 8 bytes
  ip (optional)	-> 8 bytes
  cookie2	-> 8 bytes
  cookie1	-> 8 bytes

The offset of the cookie for the current bpf program, which is in 8-byte
units, is stored in the
"(((u64 *)ctx)[-1] >> BPF_TRAMP_COOKIE_INDEX_SHIFT) & 0xFF". Therefore, we
can get the session cookie with ((u64 *)ctx)[-offset].

Implement and inline the bpf_session_cookie() for the fsession in the
verifier.

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
Link: https://lore.kernel.org/r/20260124062008.8657-6-dongml2@chinatelecom.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Menglong Dong 2026-01-24 14:20:00 +08:00 • committed by Alexei Starovoitov
parent 27d89baa6d
commit eeee4239db
2 changed files with 35 additions and 0 deletions
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15
include/linux/bpf.h
View file

@ -1229,6 +1229,7 @@ enum {
#endif
};
#define BPF_TRAMP_COOKIE_INDEX_SHIFT 8
#define BPF_TRAMP_IS_RETURN_SHIFT 63
struct bpf_tramp_links {
@ -1782,6 +1783,7 @@ struct bpf_prog {
enforce_expected_attach_type:1, /* Enforce expected_attach_type checking at attach time */
call_get_stack:1, /* Do we call bpf_get_stack() or bpf_get_stackid() */
call_get_func_ip:1, /* Do we call get_func_ip() */
call_session_cookie:1, /* Do we call bpf_session_cookie() */
tstamp_type_access:1, /* Accessed __sk_buff->tstamp_type */
sleepable:1; /* BPF program is sleepable */
enum bpf_prog_type type; /* Type of BPF program */
@ -2190,6 +2192,19 @@ static inline int bpf_fsession_cnt(struct bpf_tramp_links *links)
return cnt;
}
static inline int bpf_fsession_cookie_cnt(struct bpf_tramp_links *links)
{
struct bpf_tramp_links fentries = links[BPF_TRAMP_FENTRY];
int cnt = 0;
for (int i = 0; i < links[BPF_TRAMP_FENTRY].nr_links; i++) {
if (fentries.links[i]->link.prog->call_session_cookie)
cnt++;
}
return cnt;
}
int bpf_prog_ctx_arg_info_init(struct bpf_prog *prog,
const struct bpf_ctx_arg_aux *info, u32 cnt);

20
kernel/bpf/verifier.c
View file

@ -14406,6 +14406,9 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
return err;
}
if (meta.func_id == special_kfunc_list[KF_bpf_session_cookie])
env->prog->call_session_cookie = true;
return 0;
}
@ -23024,6 +23027,23 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
insn_buf[1] = BPF_ALU64_IMM(BPF_RSH, BPF_REG_0, BPF_TRAMP_IS_RETURN_SHIFT);
insn_buf[2] = BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 1);
*cnt = 3;
} else if (desc->func_id == special_kfunc_list[KF_bpf_session_cookie] &&
env->prog->expected_attach_type == BPF_TRACE_FSESSION) {
/*
* inline bpf_session_cookie() for fsession:
* __u64 *bpf_session_cookie(void *ctx)
* {
* u64 off = (((u64 *)ctx)[-1] >> BPF_TRAMP_COOKIE_INDEX_SHIFT) & 0xFF;
* return &((u64 *)ctx)[-off];
* }
*/
insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
insn_buf[1] = BPF_ALU64_IMM(BPF_RSH, BPF_REG_0, BPF_TRAMP_COOKIE_INDEX_SHIFT);
insn_buf[2] = BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xFF);
insn_buf[3] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_0, 3);
insn_buf[4] = BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1);
insn_buf[5] = BPF_ALU64_IMM(BPF_NEG, BPF_REG_0, 0);
*cnt = 6;
}
if (env->insn_aux_data[insn_idx].arg_prog) {